CODEWITHSUNDEEP
concurrencyjava-8
michealAtmi
michealAtmi

Reputation: 1042

CompletableFuture.allOf, logging and rethrowing exception

I have a set of futures, each of which may throw an exception that I want to log in my way and rethrow, but this doesn't compile:

 CompletableFuture<Void> lordOfFutures = CompletableFuture.allOf(future1, future3, future2)
            .handle((screen, throwable) -> {
            if (throwable!=null) {
                LOG.error(throwable, throwable);
                throw throwable;
            } else {
                return screen;
            });

Is it possible to log the first exception that occurs and rethrow it?

Upvotes: 0

Views: 780

Answers (1)

Holger
Holger

Reputation: 298233

handle expects a BiFunction<? super T,Throwable,? extends U> whose apply method is not allowed to throw Throwable. This applies to all functions of the java.util.function package. But you don’t need to rethrow the throwable at all:

CompletableFuture<Void> lordOfFutures = CompletableFuture.allOf(future1, future3, future2)
    .whenComplete((screen, throwable) -> {
        if (throwable!=null) {
            LOG.error(throwable, throwable);
        });

The future returned by whenComplete will have the same completion state or value as the future you’re calling it on (but only after executing the specified action). So if the future returned by allOf gets completed exceptionally, the “lordOfFutures” will be too, and otherwise, it will be completed with the same value (which is always null here).

Upvotes: 1

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